I agree. When I want to maintain mosses outside an aquascape I put them in a flattish plastic container with a clear lid. I put a layer of Fluval substrate or ADA Aquasoil on the bottom, them saturate it with water. Then I just lay the moss on top of the wet soil and close it up. I keep it in a bright room, with INDIRECT sun light. It is never in direct sunlight. I have found that mosses do very well this way, and reproduce readily.

I have not had good luck growing even "easy" mosses on the windowsill. I think they get too warm in the sun light.

Interesting can I grow them stacked plastic container on plastic container? I've never tried emersed how saturated does the substrate have to be and how easily does it adapt to submersed life when you want to put it into the tank?